Embedded memory devices fabricated with trench capacitors and/or vertical transistor cells have benefits over planar-stacked device structures. Trench capacitors have replaced the planar storage capacitor in order to meet the scaling demands for high performance DRAM (dynamic random access memory) cell production.
A trench capacitor is a three dimensional device formed by etching a trench into a semiconductor substrate. After trench etching, a buried plate electrode is formed about the exterior portion of the trench and a node dielectric is then formed on the inner walls of the trench. The trench is then filled, for example, with N-type polycrystalline silicon (“N-type Poly-Si”). In order to obtain sufficient capacitance, a dopant level of about 1019 atoms/cm3 is commonly utilized. The doped Poly-Si serves as one electrode of the capacitor, often referred to as the upper electrode or storage node. An N-type doped region surrounds the lower portion of the trench, serving as the second electrode and is referred to as the lower electrode or a “buried plate” or “diffusion plate”. A node dielectric separates the buried plate and the upper electrode and serves as the insulating layer of the capacitor.